When Is Black Mold Toxic?

Numerous species of molds can grow inside a home, most of which are not harmful to humans and only present cosmetic and sanitary concerns. Some select species, however, can have toxic health effects on humans after prolonged exposure. It is nearly impossible for a layperson to identify a mold species as benign or toxic simply by looking at it, but it is still important to know when a mold is considered toxic and when it is not.

Mold Toxicity

Though some molds are known colloquially as "toxic molds," this is actually a misnomer. No mold species is itself toxic, but some species are capable of producing toxic substances called mycotoxins. It is exposure to these mycotoxins that can cause deleterious health effects rather than exposure to the mold itself. Still, those species known as "toxic molds" are those capable of producing mycotoxins.

Black Molds

One species of mold in particular -- Stachybotrys chartarum or Stachybotrys atra -- is known to be a mycotoxin producer, and thus is known colloquially as "black mold" or "toxic mold." Stachybotrys chartarum is a greenish-black mold that tends to grow on moist areas that are high in cellulose content and low in nitrogen content, like fiberboard, gypsum board, paper, dust and lint. Note that despite its colloquial name, Stachybotrys chartarum is not always black, and black molds are not always Stachybotrys chartarum.

Health Effects

Exposure to Stachybotrys chartarum can cause coldlike symptoms, including eye, nose, throat and skin irritation. These symptoms will be exacerbated in those with diminished immune system function, those with chronic respiratory conditions or those with sensitive mold allergies. A comprehensive study by the Institute of Medicine (IOM) found scientific evidence for linking Stachybotrys chartarum exposure to "upper respiratory tract symptoms, cough, and wheeze in otherwise healthy people...asthma symptoms in people with asthma...hypersensitivity pneumonitis in individuals susceptible to that immune-mediated condition...[and] respiratory illness in otherwise healthy children."

Removal Methods

The good news is that Stachybotrys chartarum can quickly and safely be removed in a few simple steps. Simply clean and disinfect the area in which the colony is growing with a household cleaner or disinfectant and allow it to dry thoroughly (you can use a solution of 1 cup bleach to 1 gallon water as a disinfectant). Most importantly, always remove any sources of excess moisture like malfunctioning air conditioner equipment, leaky plumbing or a broken water heater. A failure to do so will likely result in future mold colonies growing in the same area.